The invention relates generally to apparatuses and methods for cutting porous substrates.
Porous substrates, such as cellulose matrices (e.g. 31 ETF, FTA and FTA elute cards available from Whatman) are often used to store biological samples, such as blood. A new application area for these cards is in the pharmaceutical industry, which is using them to store dried blood samples from pharmacokinetic and toxicokinetic studies. When it is time to analyze the amount of drug or drug metabolite in the dried blood spot, the current methods require the user to cut the sample out of the card, usually a 1-6 mm diameter circle, place the cut disc in a vial or well with extraction fluid, and then shake/vortex for a set period of time. The extraction fluid is then removed and analyzed using a method such as LC-MS.
The pharmaceutical industry is expecting to process a large number of samples per day and is therefore looking for ways to automate the process. However, unlike typical blanking or punching operations, the stock material used in such processes is not fed from a roll-to-roll system. The FTA cards typically contain 1-4 samples locations and thus must be handled individually, even when high-throughput processing is required. Additionally, the desired punch location can vary from card to card. Thus, the cards are typically manipulated and positioned by a robotic end effector or mechanism to move the cards to the correct location with respect to the punch. To allow for high-density card storage, the card gripper fingers should be as thin as possible. However, very thin gripper fingers are unlikely able to prevent the punch retraction forces from moving or pulling the card from the gripping system. Thus the integration of a stripping sleeve with the punch prevents motion of the paper. Additionally, as a variety of card types exist, the stripping sleeve is essentially independent of the desired card type to be punched.
One approach to preventing card motion during punching or retraction is to create a stiff gripper that substantially encompasses the perimeter of the FTA card and prevent the card from being pulled up/out during the retraction process. However, the design limits the storage density of the cards and must be custom designed for each new card shape.
Another problem associated with automated the sample processes systems that comprise disc cutting and extraction is that the tiny discs are highly prone to the effects of static electricity or even a light breeze. There are numerous reports of cut discs being lost during the cutting step or during transport of the cut discs. Currently, sample discs are lost due to factors such as static electricity and air movement. For example, static charges may build up in the plastic multiwall plates or tubes, causing the discs to sticks to the plates or tubes walls. The discs sometimes stick to the punching device, or, later in the process, the discs sometimes stick to the liquid handling probes, which, when the probes are withdrawn from the well, the discs are inadvertently removed from the well. The current instruments on the market focus on reducing sample disc loss by reducing the amount of air movement in the system (enclosed system) and adding anti-static devices (such as humidifiers).